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Jeffrey M. Levsky, MD, PhD; Matthew P. Moy, MD; Linda B. Haramati, MD, FCCP
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From the Albert Einstein College of Medicine & Montefiore Medical Center (Drs Levsky and Haramati); and Massachusetts General Hospital (Dr Moy).

Correspondence to: Jeffrey M. Levsky, MD, PhD, Albert Einstein College of Medicine, Montefiore Medical Center, 111 E 210 St, Bronx, NY 10467; e-mail: jlevsky@montefiore.org


Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2013;143(6):1839-1840. doi:10.1378/chest.13-0569
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To the Editor:

We thank Drs Hu and Zhong for their thoughtful letter regarding our article on estimating pleural effusion size on CT scans.1 We are happy to further clarify our reasoning for grouping effusions by percentage of the hemithorax volume into small (<20%), moderate (20%-40%), and large (>40%).

Since no exact threshold accurately predicts an outcome or obligates specific management, any selection of cutoffs is arbitrary, whether based on fraction of the hemithorax or actual volume. Separation into thirds2 or use of quartiles, as suggested by Drs Hu and Zhong, are both, to our knowledge, without precedent. We designed our cutoffs rationally, with no a priori assumptions, based on the ability of the best CT imaging features to consistently separate effusions into groups.1 The rule was engineered for ease of use.

It is true that a common plain radiographic classification system uses cutoffs of <500 mL, 500 to 1,000 mL, and >1,000 mL.3 We agree that this is a logical starting point for a rule based on CT imaging. However, we avoided a method based on raw volume for two major reasons. First, we found a weaker association between absolute effusion volume and the CT imaging features, as well as inconsistencies in the relationship of absolute volume to percentage volume. For example, small effusions ranged from 78 to 328 mL, moderate effusions ranged from 378 to 1,566 mL, and large effusions ranged from 472 to 3,673 mL (data not previously shown). Second, we firmly believe that the physiologic effect of a pleural effusion of any given volume depends on the patient’s body habitus. It is hard to imagine that a 500-mL effusion in a small, elderly woman is as well tolerated as the same volume in a hulking male athlete. In fact, our data support this common sense conclusion, as the typical geometry of the layering effusion better reflects the volume percent rather than the raw volume. Thus, the effusion percent allows a better fit for the data and a more physiologic representation of disease severity.

Clinical medicine is replete with cutoffs in laboratory values, diagnostic criteria, treatment algorithms, and staging rules that undergo regular reevaluation. We claim no monopoly on assessment of pleural effusions, a disease process defined by gradations of increase from the physiologic amount of pleural fluid. The system we proposed yields an expedient and easily taught method for quantifying pleural effusions, thus advancing communication and reproducibility.

References

Moy MP, Levsky JM, Berko NS, Godelman A, Jain VR, Haramati LB. A new, simple method for estimating pleural effusion size on CT scans. Chest. 2013;143(4):1054-1059. [PubMed]
 
Mironov O, Ishill NM, Mironov S, et al. Pleural effusion detected at CT prior to primary cytoreduction for stage III or IV ovarian carcinoma: effect on survival. Radiology. 2011;258(3):776-784. [CrossRef] [PubMed]
 
Evans AL, Gleeson FV. Radiology in pleural disease: state of the art. Respirology. 2004;9(3):300-312. [CrossRef] [PubMed]
 

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Tables

References

Moy MP, Levsky JM, Berko NS, Godelman A, Jain VR, Haramati LB. A new, simple method for estimating pleural effusion size on CT scans. Chest. 2013;143(4):1054-1059. [PubMed]
 
Mironov O, Ishill NM, Mironov S, et al. Pleural effusion detected at CT prior to primary cytoreduction for stage III or IV ovarian carcinoma: effect on survival. Radiology. 2011;258(3):776-784. [CrossRef] [PubMed]
 
Evans AL, Gleeson FV. Radiology in pleural disease: state of the art. Respirology. 2004;9(3):300-312. [CrossRef] [PubMed]
 
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